1. Field of the Invention
This invention relates to providing a substrate with a surface having an area part of which has good solvent-wettability and another part of which has poor solvent-wettability, e.g. so that a solvent which comes into contact with the area tends to concentrate on the first-mentioned part while the second-mentioned part remains essentially dry.
2. Description of Related Technology
One application for the process of the invention is in the field of drop-on-demand ink jet printers of the kind having a printhead which includes an array of nozzles through which liquid ink drops are ejected on demand on to a surface to be printed.
In one design of printhead, which is described in our copending UK application No. 8810241.3 and in published European Patent Application No. 339,926 (Nov. 2, 1989), the nozzles are formed in the head itself or on a separate nozzle plate which is mounted on the head, and a house-keeping manifold is located on the head or on the nozzle plate for supplying environmental fluids to or exhausting such fluids from the region of the orifices. In one embodiment of this design of printhead, it is desirable for at least an annular zone surrounding each orifice to be substantially non-wettable by the ink employed and for at least a part of the remaining surface of the head (or nozzle plate where used) to be wettable so that the manifold may be bonded securely to the head (or nozzle plate).
In another design of printhead, it can be desirable for a small area of the head or nozzle plate adjacent each orifice to have a surface which is readily wetted by the ink and for another area immediately surrounding that area to be essentially non-wettable.
It is known that many organic compounds containing chemically combined fluorine, e.g. fluoropolymers and polyfluorinated organic compounds, can provide surfaces which have generally very poor solvent-wettability; see, for example, U.S. Pat. Nos. 4,368,476 and 4,643,948 and published European Application No. 177,316. However it is difficult to bond them adequately to many substrates.
The problem is particularly acute with the high softening point plastics materials, especially the condensation polymers having aromatic groups such as polyimides, polycarbonates, polysulphones, polyesters and polyether ether ketones, which are favoured for the production of printheads and nozzle plates of drop-on-demand ink jet printers.
We have found that the adhesion of such compounds, hereinafter referred to as organic fluorocompounds, to substrates, and especially the aforementioned high softening point plastics materials, may be improved by use of a keying interlayer of siloxic material, by which we mean a material made up mainly of silicon atoms linked together by oxygen atoms; i.e. having --Si--O--Si--groups.
However, the formation of zones having good solvent wettability and zones having poor solvent wettability from such a system on printheads or nozzle plates of drop-on-demand ink jet printers using conventional techniques has presented difficulties.
Specifically, the use of a stand-alone mask to protect areas of the printhead which are not to be coated is generally precluded because the liquid material favoured for forming the siloxic layer tends to creep under it. The alternative of an adhesive mask, on the other hand, is precluded by the tendency of such masks to dimensional instability which is exacerbated by the miniature scale of the operation. Distances between adjacent zones which are to be coated may be of the order of only tens of microns.
At this miniature scale, the fact that feature sizes are limited by the thickness of the mask presents yet a further limitation since at mask thicknesses which enable zones of the desired size to be coated, the mask tends to be too fragile.
Deposition of masks by painting or printing has also proved impracticable.
Yet a further problem is that the contours produced by the use of a mask tend to cause unacceptable differences in the thickness of the siloxic layer which can be exacerbated by differences in the wettability of the surfaces of the mask and substrate, respectively, by the liquid employed to form the siloxic layer.
We have now developed a method of forming zones having good solvent wettability and zones having poor solvent wettability on a substrate such as a drop-on-demand ink jet printhead or nozzle plate in which these disadvantages are reduced or avoided.